Ridge scan antenna

ABSTRACT

An elongated horizontally disposed waveguide has a series of holes in one longitudinal side wall dimensioned below cut-off so as to be non-resonant and insensitive to wave length variations. The dimensioning and spacing of the holes on the one longitudinal side wall provides for radiation of a fan shaped beam in a vertical plane having a fairly broad elevational angle and an extremely narrow azimuth angle. The fan shaped beam itself is caused to scan through a given angle in azimuth by means of a ridge member reciprocated wholly within a new waveguide structure T shaped in cross section. In addition to the unique waveguide shape and hole design for coupling energy from the waveguide, novel input and output transition structures are provided. The waveguide is typically used in the leading edge of an aircraft wing as a radar antenna.

United States Patent [1 1 Young [11] 3,829,862 51 Aug. 13,1974

[ RIDGE SCAN ANTENNA [76] Inventor: David W. Young, 627 N.

Beechwood Dr., Burbank, Calif. 91506 [22] Filed: Apr. 20, 1973 [21]Appl. No.: 353,201

[52] US. Cl 343/767, 343/768, 343/771, 343/778, 343/854 [51] Int. ClH0lq 3/36, H01q 13/20 [58] Field of Search 343/768, 770, 771-772,343/767, 708, 778, 854, 746

[56] References Cited UNITED STATES PATENTS 2,773,256 12/1956 Ford eta1. 343/768 2,943,325 6/1960 Rotman 343/772 X 3,308,467 3/1967 Morrison,Jr. 343/771 X Primary ExaminerJames W. Lawrence Assistant ExaminerMarvinNussbaum Attorney, Agent, or Firm-Pastoriza & Kelly can [ 5 7 l ABSTRACTAn elongated horizontally disposed waveguide has a series of holes inone longitudinal side wall dimensioned below cut-off so as to benon-resonant and insensitive to wave length variations. The dimensioningand spacing of the holes on the one longitudinal side wall provides forradiation of a fan shaped beam in a vertical plane having a fairly broadelevational angle and an extremely narrow azimuth angle. The fan shapedbeam itself is caused to scan through a given angle in azimuth by meansof a ridge member reciprocated wholly within a new waveguide structure Tshaped in cross section. In addition to the unique waveguide shape andhole design for coupling energy from the waveguide, novel input andoutput transition structures are provided. The waveguide is typicallyused in the leading edge of an aircraft wing as a radar antenna.

24 Claims, 18 Drawing Figures PATENTEB I"? l 3 I974 saw 1 (f 5 Fae. 2.

P'ATE'NTEDms 13 1914 saw w s PATENTEnwc 13 I974 FIGJZ RIDGE SCAN ANTENNABACKGROUND OF THE INVENTION In my US. Pat. No. 3,389,393 entitled LOWPRO- FILE BROAD BAND MICROWAVE ANTENNA SYSTEM issued June 18, 1968 thereis disclosed a unique waveguide radar antenna preferably for use inhelicopter blades wherein an extremely narrow beam which is fan shapedin a vertical plane is generated. The rotation of the helicopter bladesthemselves effects a desired scanning operation when the antenna is usedin conjunction with a helicopter. In this respect, there are avoidedsome of the electro-mechanical difficulties associated with priorwaveguide antennas designed to scan the radiated beam; for example, thewell known eagle scanner. The eagle scanner" as well as other prior artwaveguide scanners which relied on a shifting of the phase velocity ofradiation propagated through the guide to provide a scanning pattern,normally utilized resonant slots or openings in the waveguide wallconstituting a series of antenna elements for coupling radiation out ofthe guide to form the desired beam. The basic problem involved is thefact that with such coupling out methods, the shape or geometry of thebeam became deteriorated for different scanned positrons.

The provision of a series of small closely spaced holes along alongitudinal edge of a waveguide wall such as disclosed in my heretoforereferred to U.S. Pat. No. 3,389,393 wherein the holes are dimensionedbelow cut-off so as to be non-resonant results in a unique step forwardin the art in that the phase velocity of radiation can be changed alongthe waveguide without affecting the desired radiation beam pattern. Suchan antenna would be very useful when incorporated in the leading edge ofan aircraft wing if some type of means could be provided for scanningthe particular beam configuration afforded by the closely spacednon-resonant holes.

. V scanning beam which does not suffer from large gain variations.

In my patent application Ser. No. 847,121 filed Aug. 4, 1969, now USPat. No. 3,778,821, and entitled AIRCRAFT CONTAINED PERSPECTIVE RADAR/-DISPLAY AND GUIDANCE FOR APPROACH AND LANDING, a perspective radarsystem is shown and described wherein an area of the ground ahead of anaircraft approaching for a landing is scanned by a fan shaped beam anddisplayed on a radar screen in the cockpit in such a manner as toprovide a proper perspective view to the pilot of the outlines of therunway. In this particular radar system, an antenna capable of providinga fan shaped beam in a vertical plane which can be scanned throughbroadside in azimuth with no appreciable degradation of the beam patternis most desirable.

While the desired narrow beam pattern in a vertical plane can beachieved by providing a relatively long radiating waveguide, scanningsystems for altering the I phase velocity of the propagated radiationthrough the guide in order to effect a proper scanning as knownheretofore have not been adequate, particularly for use with theperspective radar system described in my above referred to co-pendingapplication.

BRIEF DESCRIPTION OF THE PRESENT INVENTION its radiated beam pattern. Inaddition, the design is such that an extremely low profile structureresults permitting installation of the antenna on any elongated surfaceportion of an aircraft such as the leading edge of an aircraft wing.

Briefly, the antenna system comprises an elongated horizontally disposedwaveguide for receiving electromagnetic energy in one end and having aseries of holes in one longitudinal side wall dimensioned below cut-offI so as to be non-resonant and insensitive to wave length variations,the holes coupling energy out from the waveguide in a manner definingthe desired fan shaped beam. To effect scanning, an elongated ridgemember essentially co-extensive with the length of the waveguide ispositioned within an interior structural portion of the guide alongitsIength. Means are then provided for maintaining the leading edge ofthe ridge in parallel relation with the longitudinal axis of thewaveguide while moving the ridge towards and away from one wall of thewaveguide to thereby vary the phase velocity of energy propagated alongthe waveguide in a manner to effect scanning of said fan shaped beamthrough said given azimuth angle.

Important features of the invention in various embodiments disclosedrelate to the geometry of the cross section of the waveguide and theseries of holes. In the embodiment in which scanning is effected throughbroadside, the series of holes are arranged in first and second groupsdisposed alternately above and below the longitudinal center line of alongitudinal side wall of the waveguide. Thespacing of the groups issuch that scanning can take place through broadside. By providing aunique waveguide shape in the form of an extruded T in cross section,the ridge member utilized for effecting the scanning is arranged toessentially float in the stem portion of the T and can furthermoreassume negative positions with respect to conventional rigid ridgedwaveguide shapes.

Further features have to do with coupling of energy through the holesfrom the waveguide to free space in an efficient manner and in theprovision of unique input and termination transition structures for thewaveguide antenna to provide for maximum efficiency in the use of theelectromagnetic energy and minimize the overall dimensions of thewaveguide.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and further features andadvantages of the ridge scan antenna of this invention will be betterunderstood by now referring to the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of an aircraft incorporatingthe ridge scan antenna of the present invention in a leading edge of oneof the wings;

FIG. 2 is an enlarged fragmentary perspective view of an extrusionforming the elongated waveguide antenna incorporated in the leading edgeof the wing in FIG. 1;

FIG. 3 is a fragmentary cross section taken in the direction of thearrows 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary view partly in cross section showingan end view of the waveguide ridge scan antenna incorporated in theleading edge of the aircraft wing of FIG. 1;

FIG. 5 is a fragmentary perspective view of dielectric coupling elementsassociated with the waveguide structure of FIG. 4;

FIG. 6 is a bottom plan view partly in cross section looking in thedirection of the arrows 66 of the structure of FIG. 4;

FIG. 7 is a fragmentary broken away perspective view of an inputtransition structure for the antenna;

FIG. 8 is a fragmentary broken away perspective view of a terminationtransition structure for the antenna; 1

FIG. 9 shows a modified input transition structure; FIG. 10 shows amodification of the structure of FIG.

FIG. 11 is a fragmentary broken away perspective view of a modifiedtermination transition for the antenna;

FIG. 12 shows yet another embodiment of an input means for feedingenergy into the antenna;

FIG. 13 is a cross section of a termination for use with the input shownin FIG. 12;

FIG. 14 is a fragmentary perspective view partly broken away of amodified hole arrangement in the antenna of the present invention;

FIG. 15 is an end view of the antenna partially in cross section showingits position in the leading edge of an aircraft wing;

FIG. 16 is a plan view of an aircraft incorporating the antenna of FIG.15 in its wing;

FIG. 17 is a fragmentary perspective view showing fixed phase shiftmeans associated with an embodiment of the antenna of the invention;and,

FIG. 18 is a fragmentary perspective partly broken away showing asegmented ridge structure for the antenna.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1 there isshown an aircraft 10 having a leading edge wing portion 11 incorporatingthe ridge scan antenna of the present invention. This leading edge 11includes an elongated aperture extending in a horizontal direction andvisible from a front line of sight parallel to the axis of the aircraft.The radiated beam is fan shaped in a vertical plane as indicated at 12and is fairly broad in elevation as indicated by the angle a. The widthof this fan shaped beam indicated at W is extremely small and isnormally determined by the overall length of the elongated waveguideantenna itself in the wing portion 11. For the particular waveguideantenna to be described, scanning of the fan shaped beam 12 can takeplace through broadside; that is, through a given azimuth angle 0 oneither side of a plane perpendicularly bisecting the antenna.

Typically, the elongated waveguide behind the aperture 11 may be of theorder of 102 inches to provide a beam width W of (17. The elevationalangle a of the fan shaped beam may be 25 and the azimuth scan angle oneither side of broadside indicated at 6 may typically be i 15.

Referring now to FIG. 2, in accord with an important feature of thisinvention, the entire waveguide antenna may constitute an aluminumextrusion 13, the waveguide housing portion being Tshaped as indicatedat 14 with two opposite longitudinal broad side walls 15 and 16 and twoopposite longitudinal narrow side walls 17 and 18 making up the cross ofthe T and a portion 19 making up the stem of the T.

In the embodiment shown in FIG. 2, one longitudinal side wall of thewaveguide shown as the broad side wall 16 includes a series of holes 20arranged in first and second groups disposed alternately above and belowthe longitudinal center line of the side wall. Each of the groups isformed in a recessed area to define a reduced thickness portionsurrounding a given number of holes making up the group. The recessedareas for the various groups are shown at 21, 22, 23, 24, and so forth.

The given number of holes in each group are closely spaced in side byside relation along a given longitudinal distance to define a givenlength for the group. As shown in FIG. 2, the spacing between successivegroups is of the same order as the given length of any one group.

The small holes making up each group are dimensioned below cut-off so asto be non-resonant and when arranged in the configuration shown in- FIG.2, energy is coupled out of the waveguide in such a manner that thegiven azimuth angle of scan passes through broadside.

FIG. 3 shows in fragmentary cross section a detail of the holes 20 andrecessed area 21 providing the reduced wall thickness for couplingenergy from the guide. Since the diameters of the holes cause them to bebeyond cut-off in the region of the operating frequency, theoreticallythe holes are so small as to act as small round waveguides operated atcut-off which do not propagate but exhibit stable high loss per inch inthe cut-off region. Nevertheless and what constitutes a non-obvious andimportant discovery, is the fact that the waveguide functions as aradiative waveguide, the cross section, reduced wall thickness(typically 010 inches) and distribution of the holes being such as toprovide the desired coupling and radiation beam pattern of extremelynarrow width in a direction parallel to the axis of the waveguide andfairly broad in elevation. The reduced wall thickness to substantiallyless than one inch greatly reduces the loss per inch" factor.

Referring again to FIG. 2, increased efficiency in coupling energy fromthe waveguide through the holes and combining the energy from lower andupper hole groups is achieved by providing integral upper and lowerlongitudinal flanges 25 and 26 extending forwardly from the upper andlower edges of the longitudinal broad side wall 16 to define extendedconductive surfaces guiding the coupled out radiant energy in a forwarddirection. These flanges as shown may constitute part of the overallextrusion and further serve as a securing means for mounting thewaveguide in the leading edge of the wing.

The concept of providing a complete extrusion significantly minimizesany leakage of electromagnetic energy in portions of the waveguide otherthan the holes.

Referring now to FIG. 4, the manner in which the ex trusion of FIG. 3 isdisposed in the leading edge 11 of the wing of the aircraft in FIG. 1will become evident. As shown, there may be provided simple screws 27and 28 securing the extended portions making up the flanges and 26 tothe leading edge portions of the wing. Further openings such asindicated at 29 and 30 may be provided for receiving suitable mountingmeans at the end portions of the elongated waveguide.

In addition to the extruded member 13 itself making up the waveguide,there is shown in FIG. 4 a means for scanning the resulting fan shapedbeam in accord with the present invention. In this respect, it will benoted that the housing 19 forming the stem of the T-shaped extrusionportion of the guide intercepts the broad side wall 15 to define an openelongated slot 31. An elon gated ridge member 32 coextensive with thelength of the radiating portion of the waveguide is arranged to remainin the interior of the guide with a portion partially in slot 31. Meansare then provided for maintaining the leading edge of the ridge 32 inparallel relation with the longitudinal axis of the waveguide whilemoving the ridge towards and away from the opposite side wall 16 tothereby vary the phase velocity of energy propagated along the waveguidein a manner to effect scanning of the fan shaped beam through the givenazimuth angle.

The foregoing means for moving the ridge member includes a series ofrods one of which is indicated at 33 rigidly secured at first ends tothe trailing edge of the ridge member at evenly spaced longitudinalpoints, the other ends of the rods passing through bearing openings 34in the housing 19 to be coupled to a driving means designated generallyby the number 35.

In the particular embodiment shown in FIG. 4, the driving means 35includes a reciprocating yoke member 36 to which the extending ends ofthe rods 33 are secured as at 37. The yoke 36 reciprocates in guidewalls or tracks 38 and 39 by action of a rotating shaft 40 having aneccentric disk 41 within an oblong opening 42 of the yoke 36. From thedotted line designations, it will be appreciated that when the shaft 40is rotated by any suitable motor means, the eccentric cam 41 willessentially drive the yoke 36 back and forth between the walls 38 and 39to thereby move the rods 33 and ridge member 32 in a back and forthmotion.

An important feature of this ridge construction resides in the fact thatthe ridge member 32 itself and rods are held out of physical contactwith the housing of the waveguide other than at the points where therods pass through the bearings 19 so that the ridge is essentiallyfloating." No chokes are required to concentrate the energy between theridge and broad wall 16 when the proper transition is used to assure apure mode.

A further important feature is the fact that the housing 19 which formsthe stem of the T shaped waveguide is sufficiently long that the ridgecan move freely to a negative ridge position with respect to aconventional rigid ridged waveguide shape. Thus, as indicated by thesmall letter (1" the leading edge of the ridge 32 actually moves beyondthe slot 31 to be outside of a conventional rigid ridged waveguideshape. The negative ridge feature provides for a greater range of phaseshift of the velocity of the propagated radiation down the guide tothereby increase the azimuth scanning angle. The reciprocation of therods 33 and ridge 32 to move the leading edge of the ridge membertowards and away from the opposite broad side wall 16 of the waveguideis indicated by the double headed arrow 43.

Referring now to the front portion of the side wall 16 between theconducting flange surfaces 25 and 26 through which radiation is coupledfrom the guide, there is shown an elongated plastic means in the form ofa strip 44 and a secondary backing plastic strip 45 having dielectricconstants of typically 2.0 and 4.0 to effect an optimum coupling of theenergy passing from the holes in the waveguide to free space. The areain front of the strips may be filled with foam 46 and a suitablefiberglass radome 47 provided between the front exit portions of theflanges 25 and 26 contoured aerodynamically to conform with the leadingedge of the wing 11.

In the end view of the extrusion 13 of FIG. 4, there are providedlongitudinally extending lightening passages 48 and 49 parallel to andon either side of the narrow sides or walls 17 and 18 of the waveguide14. Advantage may be taken of these or similar passages for de-icingpurposes by simply passing hot air through the passages to heat theextrusion.

Referring to FIG. 5, the dielectric plastic strips 44 and 45 are shownin perspective wherein it will be noted that the strip portion 44includes on its face forward projecting ridges 50 which fit in therecessed areas such as the area 21 of FIG. 4 provided for the holes 20.In this respect, it is important that the plastic be in surface contactwith the exit peripheral portions of the holes to effect the desiredcoupling of the energy to free space. These same plastic strips can alsoserve a further function in the event de-icing is'desired but whereinlightening passages such as 48 and 49 described in FIG. 4 are notavailable or are not used. This alternate de-icing system comprises theprovision of a conductive path 51 on the front face of the plastic strip44 following a circuitous route to pass between the ridge portionsfilling the recessed areas on either side of a center line from one endof the plastic strip towards the other. Current can be passed throughthe conductive path to thereby heat the extrusion and again serve as ade-icing means.

FIG. 6 shows in bottom plan and in partial cross section the variouscomponents described in FIG. 4. In this FIGURE there is schematicallyindicated a motor coupled to rotate the shaft 40 and thus effectsimultaneous reciprocation of the various rods 33 to move the ridge 32towards and away from the opposite waveguide wall 16. The reciprocatingmotion of the ridge by the means shown in FIGS. 4 and 5 assuming thatthe motor of FIG. 5 rotates at a constant speed would be sinusoidal sothat scanning of the fan shaped beam back and forth between the azimuthangle limits would be sinusoidal. Pure sinusoidal scanning will minimizethe generation of mechanical harmonics. On the other hand, there is somedwell time of the scanning beam at the limits of the scan where itreverses direction. Further if a strictly sinusoidal scan is provided,the motion of the scanning beam is non-linear from one extreme to theother. With the arrangement shown in FIGS. 4 and 5,. the nonlinearitythroughout the scanning sweep can be corrected by simply providing amotor which does not rotate at a constant speed but rather rotates theshaft 40 with a varying speed in such a manner that the rods 33 andridge 32 move in their back and forth directions at a constant speed.Such variable speed motors such as stepper type motors are readilyavailable and it is accordingly to be understood that the driving meansmotor depicted in FIG. could be a variable speed motor thereby providingmeans for reciprocating the rods to follow a linear motion over a majorportion of their travel in each direction.

Another means of effecting linear travel would be to reshape theeccentric shaped cam 41 in such a manner that when the shaft 40 isrotated at a constant speed, the shaping of the cam will urge the yoke36 and rods 33 in back and forth motion which constitutes over a majorportion of the travel in each direction a linear motion.

Referring now to FIG. 7, there is shown an input energy transitionstructure for passing electromagnetic energy into one end of thewaveguide 14. This. input transition structure includes an inputwaveguide section 52 having a transition ridge section 53 pivoted at oneend as at 54 to the coextensive end of the ridge member 32 in thewaveguide 14. The other end of the transition ridge section 53 in turnis coupled as by a pivot pin 55 which can ride in a slot 56 in such amanner that the top end surface 57 of the ridge section is generallyflush with the wall 58 through which the ridge extends.

With the foregoing arrangement, a gradual diminu tion of the effect ofthe ridge member is provided for any given position of the ridge memberfor the electromagnetic energy passing into the main waveguide 14.

In addition, the input energy transition structure shown includes anexpanding waveguide coupling section 59 with its convering end coupledto the input waveguide section as at 60 and its expanded end 61 properlydimensioned to receive input electromagnetic energy carried in astandard sized waveguide for the particular operating frequency.

To minimize reflections at the other end of the elongated waveguide, asimilar termination transition structure is provided. Thus, referring toFIG. 8 there is shown a termination waveguide section 62 having atransition ridge section 63 pivoted at- 64 to the end of the ridgemember coextensive with the other end of the waveguide 14. The other endof the termination transition ridge section is coupled as by pivot pin65 and cooperating slot 66 in such a manner that its top surface will beflush with the wall of the termination waveguide section so that again agradual diminution of the effect of the ridge member is provided for anygiven position of the ridge member. This termination structure alsoincludes a wedge shaped section of ferrite material 67 on the wall ofthe termination waveguide section 62 opposite to the transition ridgesection to minimize reflections of energy, the waveguide section 62itself being closed at its extreme end as by a metal plate 68.

FIGS. 9, 10, and 11 illustrate alternative input and terminationtransition structures to those described in FIGS. 7 and 8.

Considering first the input transition structure shown in FIG. 9, thereis provided an input waveguide section 69 within which there is anintegral extension of the ridge member 32 for the main waveguide 14,this ridge member being designated 32' in FIG. 9. The integral extensionof the ridge member is shown at 70, its upper edge tapering towards itslower edge and including a plurality of slots 71 to define ridgeprojections 72 decreasing successively in height. The floor of the inputwaveguide section 69 in turn includes a series of windows 73 or openingsthrough which the ridge projections 72 extend when the ridge member ismoved into and out of the waveguide. The effect of this arrangement isto provide a gradual diminution of the effect of the ridge member forany given position of the ridge member and has the advantage of avoidingrelatively moving ridge section parts such as is the case with thepivoted structure of FIG. 7. In the input transition structure of FIG. 9there is again provided an expanding waveguide coupling section 59 withits converging end connected at 60 to the input waveguide section 69 andits expanded end 61 receiving input electromagnetic energy. Since thisexpanding waveguide section is identical to that shown in FIG. 7, thesame numerals have been used.

In order to minimize the overall length of the antenna, the inputwaveguide section 69 itself may constitute an expanding waveguidesection.

FIG. 10 shows such an expanding waveguide section at 74 wherein theexpanding lower wall includes a series of windows 75 for receiving theridge projections 72 of the tapered integral ridge 70.

FIG. 11 illustrates a termination transition structure utilizing aslotted tapered transition ridge in place of the pivoted ridge sectiondescribed in FIG. 8. Thus, the termination waveguide section is shown at76 having an integral tapered ridge section 77 slotted at 78 to defineridge projections 79 passing up through a series of windows 80 in thetermination section 76. A wedge shaped section of ferrite 67 andmetallic closure end plate 68 is provided for the termination waveguide76, these latter elements being identical to the wedge section andclosure plate 67 and 68 described in FIG. 8.

Further shortening of the overall length of the waveguide antenna can beaccomplished by eliminating transition structures such as described inthe previous drawings and feeding electromagnetic energy into the mainwaveguide by a coaxial line. Such an input structure is illustrated inFIG. 12 wherein the one end of the main waveguide 14 to receiveelectromagnetic energy includes an input waveguide section 81 having aridge section designated 32" which constitutes an integral part of theridge member 32 in the main wave guide I4. The upper wall of thewaveguide section 81 opposite the ridge portion 32" has a coaxial linecomprised of an outer conductor 82 terminating at the wall of thewaveguide 81 and an inner conductor 83 extending into the waveguidetowards the top edge of the ridge section 32". This inner conductor 83terminates short of the leading edge of the ridge section.

In order that input electromagnetic energy in the coaxial line istransferred to the waveguide with maximum coupling efficiency for everyposition of the ridge member, it is necessary to provide a movabletuning probe means extending into the wall of the waveguide sectionwhich in the example shown in located at 84 between the inner conductor83 and the remaining elongated portion of the waveguide 14. This tuningprobe means may take the form of a probe structure having two spacedprobes 85 extending into the waveguide parallel to the inner conductor83 of the coaxial line. The probes 85 are caused to move in and out ofthe waveguide in synchronism with movement of the ridge,

any suitable mechanical connection 86 between the probe structure 84 andthe ridge 32 accomplishing this desired result. The use of the probes isintended to follow well known theory in the use of tuning screws tominimize the voltage standing wave ratio.

By utilizing a coaxial input for the waveguide, it will be appreciatedthat space taken up by the heretofore described transition section iseliminated.

FIG. 13 illustrates a termination arrangement which might be utilizedwith the input in any of FIGS. 7, 9, 10 or 12 to shorten the other endof the waveguide. In FIG. 13, the far end of the main waveguide 14 issimply terminated by a metallic plate 68 corresponding to the plates 68described in FIGS. 8 and 11. In addition, there is provided the wedgeshaped section 67 of ferrite material to minimize reflections, the ridgemember 32" constituting an integral extension of the main ridge member32 in the waveguide 14.

Referring now to FIG. 14, there is shown a modified waveguide antenna 87wherein a series of holes dimensioned below cut-off so as to benon-resonant extend longitudinally between the longitudinal edge of thebroad side wall of the waveguide. As shown, the portion of the wallthrough which the holes extend is recessed as at 89 to provide a reducedthickness portion as in the case of the series of holes formed in groupsdescribed with respect to the waveguide antenna 14 in FIGS. 2 and 4.However, as in the case of the antenna 14 there is provided a scanningridge member 90 within an extending housing 91 so that the same generalT shape configuration results. The ridge 90 is driven in the same manneras the ridge 32 described in the previous embodiments and thus detailsof such drive means are not shown in FIG. 14.

The configuration of the series of holes in the waveguide 87 of FIG. 14will not permit scanning of the fan shaped beam through broadside.However, there are many wing configurations in aircraft where suchscanning through broadside is not really necessary.

For example, referring to FIG. the positioning of the waveguide antenna87 in the leading edge portion of a wing is shown. The various portionsof the waveguide are designated by the same numerals used in FIG. 14.When positioned as shown in FIG. 15, the fan shaped beam will radiateout the front of the leading edge of the wing and when the ridge member90 is reciprocated, this fan shaped beam will sweep from a nearbroadside position towards the end of the waveguide opposite the endreceiving electromagnetic enll foregoing will be evident from FIG. 16which illustrates an aircraft 92 having swept back wings wherein theleading edge 93 incorporates the waveguide 87 of FIG. 15. In thisembodiment, to provide the scan in azimuth over the angle Oas indicated,the waveguide 87 is fed at its far end adjacent the top of the wing asindicated by the dashed line 94. Even though the fan shaped beam doesnot scan through broadside, in the case of a swept back wing structureas shown, the azimuth angle covered by the beam covers the desiredforward area.

FIG. 17 constitutes a modified waveguide antenna 95 similar to waveguideantenna 87 shown in FIG. 14 but wherein the series of holes are arrangedin groups such as indicated at 96 serially extending between thelongitudinal center line and one edge of the wall of the guide. Eachgroup comprises a given number of holes in closely spaced side by siderelation along a given longitudinal distance to define a given lengthfor the group. This spacing between successive groups is of the sameorder as this length. In this respect, the waveguide 95 is the same asthe waveguide 14 described in FIGS. 2 and 4 except that the groups ofholes adjacent the opposite longitudinal edge are not included. Thelongitudinal wall including the groups has recessed areas such asindicated at 97, 98, and 99 to provide reduced wall thickness portionssurrounding the holes to increase the efficiency of coupling of energyout of the waveguide.

In the waveguide antenna 95, there is additionally included a fixedphaseshift means in the form of waveguide stubs 100, 101, and 102 surroundingeach of the groups of holes and extending normally from the longitudinalwall. As in the case of the other waveguide antennas, there is provideda ridge member 103 within a housing 104 extending from the waveguide 95in a direction opposite from the wall containing the holes.

The waveguide stubs constitute fixed phase shifters having differentelectrical lengths such that the angular relationship of the limits ofthe azimuth angle through which the fan shaped beam is scanned bymovement of the ridge member 103, relative to a vertical planeperpendicularly bisecting the waveguide, can be changed.

The provision of such fixed phase shifters would enable adjustment ofthe azimuth scan angle limits depicted in FIG. 16 to accommodatedifferent geometries of swept back wings to assure that the fan shapedbeam covers the forward ground area on either side of the center line ofthe aircraft.

In all of the various embodiments described, the elongated ridge memberhas been shown as a solid bar like structure. When the length of thewaveguide antenna is of the order of ten feet, stresses tend to beestablished in the ridge member in its reciprocating movement. Relief ofsuch stresses can be achieved by segmenting the ridge member intoshorter sections to make up an overall long length.

Referring to FIG. 18, such a segmentation of the ridge member is shown.Thus, for the waveguide 14 there is illustrated segmented ridge membersections 32a, 32b, 32c within the waveguide portion 19. Suitablesevering of the ridge member to define the sections is shown at 105 and106. The solid section of the ridge 32b between the cuts would be longerthan depicted in FIG. 18.

It will be understood that the gap between the adjacent ridge sectionsat the cuts 105 and 106 is small with respect to a wave length, theresultant effect being that of a continuous ridge.

This type of ridge member construction could be utilized with the otherembodiments heretofore set forth.

It should also be understood that the slots formed in the transitionridge sections heretofore described, are

small compared to a wave length and the windows in the waveguide floorthrough which the projections of the ridge sections extend are belowcut-off. With this arrangement, the bottom wall of the stem portion 19of the waveguide can be removed as shown in some of the drawings toprovide access in the manufacture of the windows in the waveguidetransition sections.

What is claimed is:

1. A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combination:

a. an elongated horizontally disposed waveguide for receivingelectro-magnetic energy in one end and having a series of holes in onelongitudinal side wall dimensional below cut-off so as to benon-resonant, said holes coupling energy out from the waveguide in amanner defining said fan shaped beam, the non resonant characteristic ofsaid holes rendering the shape of said beam substantially insensitive tofrequency variations over approximately a frequency octave;

b. an elongated ridge member co-extensive with the length of saidwaveguide arranged to extend wholly within the guide along its length;and,

0. means for maintaining the leading edge of the ridge in parallelrelation with the longitudinal axis of the waveguide while moving theridge towards and away from the opposite side wall of the waveguide tothereby vary the phase velocity of energy propagated along the waveguidein a manner to effect scanning of said fan shaped beam through saidgiven azimuth angle.

2. A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combination:

a. an elongated horizontally disposed waveguide for receivingelectro-magnetic energy in one end and having a series of holes in onelongitudinal side wall dimensioned below cut-off so as to benonresonant, said holes coupling energy out from the waveguide in amanner defining said fan-shaped beam;

b. an elongated ridge member co-extensive with the length of saidwaveguide arranged to extend wholly within the guide along its length;and,

c. means for maintaining the leading edge of the ridge in parallelrelation with the longitudinal axis of the waveguide while moving theridge towards and away from the opposite side wall of the waveguide tothereby vary the phase velocity of energy propagated along the waveguidein a manner to effect scanning of said fan shaped beam through saidgiven azimuth angle, said series of holes being arranged in first andsecond groups disposed alternately above and below the longitudinalcenter line of said one longitudinal side wall, each group comprising agiven number of holes in closely spaced side-by-side relation along agiven longitudinal distance to define a given length for the group, thespacing between successive groups being of the same order as said givenlength whereby energy is coupled out of the waveguide in such a mannerthat said given azimuth angle of scan passes through and on either sideof a vertical plane bisecting the waveguide at its mid-point andoriented perpendicularly to the longitudinal axis of the waveguide.

3. An antenna according to claim 2, in which said one longitudinal sidewall includes recessed areas to define reduced thickness portionssurrounding the given number of holes making up the groups to increasethe effciency of coupling of energy out of the waveguide through theholes.

4. An antenna according to claim 3, in which said elongated waveguideconstitutes an integral extrusion in the form of a T in cross section,the stem of the T accomodating at least a portion of said ridge, thebroad side wall opposite the ridge constituting said one longitudinalside wall having recessed areas and said series of holes, said extrusionfurther defining integral upper and lower longitudinal flanges extendingforwardly from the upper and lower edges of the said longitudinal sidewall to define extended conductive surfaces guiding the coupled outradiant energy in a forward direction and further defining securingmeans for facilitating the mounting of the waveguide in the leading edgeof an aircraft wing, the entire extrusion minimizing any leakage ofelectromagnetic energy in portions of the waveguide other than theholes.

5. An antenna according to claim 4, including an elongated plastic meansextending longitudinally between said upper and lower flanges in surfacecontact with said one longitudinal side wall, said plastic meansincluding portions filling said recessed areas, the dielectric constantof the plastic means having a value to effect an optimum coupling of theenergy passing from the waveguide to free space.

6. An antenna according to claim 4, in which said extrusion furtherdefines longitudinal lightening passages running parallel to and oneither exterior side of the narrow sides defined by the rectangularwaveguide, whereby when said waveguide is mounted in the leading edge ofan aircraft wing, hot air can be passed through said passages to heatsaid extrusion and serve as a de-icing means for the wing.

7. An antenna according to claim 5, in which said elongated plasticmeans includes a conductive path following a circuitous route to passbetween said portions filling said recessed areas on either side of acenter line from one end of the plastic means towards the other suchthat current can be passed through the conductive path to heat theextrusion and serve as a de-icing means for the wing.

8. An antenna according to claim 1, in which said waveguide is T shapedin cross section, said one longitudinal side wall having the series ofholes constituting a broad side wall, said ridge member being positionedin the stem of said T shape for movement towards and away from saidbroad side wall, said means for maintaining the leading edge of theridge member in parallel relation with the longitudinal axis of thewaveguide while moving the ridge towards and away from the broad sidewall, including:

a. a series of rodsrigidly secured at first ends to the trailing edge ofthe ridge member at evenly spaced longitudinal points, the other ends ofthe rods passing through bearing openings in the stern of the T shape;and

b. a driving means coupled to said other ends of the rods forreciprocating them in unison back and forth in the housing to therebymove the ridge towards and away from said broad side wall, the

ridge member itself and rods being held out of physical contact with theT shaped waveguide other than at the bearing openings so that it isfloating.

9. An antenna according to claim 8, in which the stem of the T shape issufficiently long that said ridge member can move freely within the stemto a negative ridge position with respect to a conventional rigid ridgedwaveguide shape.

10. An antenna according to claim 8, in which said driving meansincludes means for reciprocating said rods to follow a linear motionover a major portion of their travel in each direction.

11. An antenna according to claim 1, having an input energy transitionstructure for passing said electromagnetic energy into said one end ofsaid waveguide, said input transition structure including:

a. an input waveguide section having a transition ridge section pivotedat one end to the co-extensive end of said ridge member in thewaveguide, and having its other end coupled to be flush with one wall ofsaid input waveguide section such that a gradual diminution of theeffect of the ridge member is provided for any given position of theridge member; and

b. an expanding waveguide coupling section with its converging endcoupled to the input waveguide section, and its expanded end receivinginput electromagnetic energy.

12. An antenna according to claim 1, having a termination transitionstructure for providing a proper termination impedance for energypassing towards the other end of said waveguide, said terminationtransition structure including:

a. a termination waveguide section having a closed end and a transitionridge section pivoted at one end to the end of the ridge memberco-extensive with said other end of the waveguide, and having its otherend coupled to be flush with one wall of said termination waveguidesection such that a gradual diminution of the effect of the ridge memberis provided for any given position of the ridge member; and

b. a wedge-shaped section of ferrite material on the wall of thetermination waveguide section opposite to the, transition ridge sectionto minimize reflections of energy at said other end of the waveguide.

13. An antenna according to claim 1, having an input energy transitionstructure for passing said electromagnetic energy into said one end ofsaid waveguide, said input transition structure including:

an input waveguide section including a transition ridge sectionconstituting an integral extension of the ridge member, said extensionhaving its upper edge tapering towards its lower edge and including aplurality of slots to define ridge projections decreasing successivelyin height, the floor of said waveguide section including a series ofwindows through which said ridge projections extend when said ridgemember is moving in the waveguide to thereby provide a gradualdiminution of the effect of the ridge member for any given position ofthe ridge member.

14. An antenna according to claim 13, in which said input energytransition structure includes an expanding waveguide coupling sectionwith its converging end connected to said input waveguidesection and itsexpanded end receiving input electromagnetic energy.

15. An antenna according to claim 13, in which said input waveguidesection expands in size from its end coupled to the waveguide to its endreceiving input electromagnetic energy. I 16. An antenna according toclaim 1, having a termination transition structure for providing aproper termination impedance for energy passing towards the other end ofsaid waveguide, said termination transition structure including: atermination waveguide section having a closed end and a transition ridgesection constituting an integral extension of the ridge member, saidextension having its upper edge tapering towards its lower edge andincluding a plurality of slots to define ridge projections decreasingsuccessively in height, the floor of said termination waveguide sectionincluding a series of windows through which said ridge projectionsextend when said ridge member is moving in the waveguide; and awedge-shaped section of ferrite material on the wall of the terminationwaveguide section opposite to the transition ridge section to minimizereflections of energy at said other end of the waveguide.

17. An antenna according to claim 1, having an input structure forpassing electromagnetic energy into said one end of said waveguideincluding:

an input waveguide section including a ridge sectionconstituting anintegral extension of said ridge member, the upper wall of the waveguidesection opposite said ridge section having a coaxial line connectedthereto, the outer conductor of the line terminating at the wall. andthe inner conductor extending into the waveguide towards the top edge ofsaid ridge section, said inner conductor terminating short of the ridgesection; movable tuning probe means extending into said wall of thewaveguide section between the inner conductor and the point ofconnection of the waveguide section to said waveguide; and meansmechanically connecting the tuning probe means to said ridge member formovement with the ridge member whereby input electromagnetic energy insaid coaxial line is transferred to said waveguide with maximum couplingefficiency for every position of the ridge member.

18. An antenna according to claim 1, having a termination transitionstructure for providing a proper termination impedance for energypassingtowards the other end of said waveguide, said terminationtransition structure including: a wedge shaped section of ferritematerial on the wall of said other end of said waveguide opposite theco-extensive end portion of said ridge member; and a metallic end wallclosing the said other end of the waveguide, the wedge shaped sectionminimizing reflections of energy at said other end of the waveguide.

19. A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combinatron:

a. an elongated horizontally disposed waveguide for receivingelectro-magnetic energy in one end and having a series of holes in onelongitudinal side wall dimensioned below cut-off so as to be non.-resonant, said holes coupling energy out from the waveguide in a mannerdefining said fan-shaped beam;

b. an elongated ridge member co-extensive with the length of saidwaveguide arranged to extend wholly within the guide along its length;and,

0. means for maintaining the leading edge of the ridge in parallelrelation with the longitudinal axis of the waveguide while moving theridge towards and away from the opposite side wall of the waveguide tothereby vary the phase velocity of energy propagated along the waveguidein a manner to effect scanning of said fan shaped beam through saidgiven azimuth angle, said series of holes extending longitudinallybetween the longitudinal center line and one edge of said onelongitudinal wall in closely spaced side-by-side relationship, theportion of the wall through which the holes pass being recessed toprovide a reduced thickness portion to increase the efficiency ofcoupling of energy out of the waveguide.

20. A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combination:

a. an elongated horizontally disposed waveguide for receivingelectro-magnetic energy in one end and having a series of holes in onelongitudinal side wall dimensioned below cut-off so as to benonresonant, said holes coupling energy out from the waveguide in amanner defining said fan-shaped beam;

b. an elongated ridge member co-extensive with the length of saidwaveguide arranged to extend wholly within the guide along its length;and,

c. means for maintaining the leading edge of the ridge in parallelrelation with the longitudinal axis of the waveguide while moving theridge towards and away from the opposite side wall of the waveguide tothereby vary the phase velocity of energy propagated along the waveguidein a manner to effect scanning of said fan shaped beam through saidgiven azimuth angle, said series of holes being arranged in groupsserially extending between the longitudinal center line and one edge ofsaid one longitudinal wall, each group comprising a given number ofholes in closely spaced side-by-side relation along a given longitudinaldistance to define a given length for the group, the spacing betweensuccessive groups being of the same order as said given length, thelongitudinal wall including recessed areas to define reduced thicknessportions surrounding the given number of holes making up the groups toincrease the efficiency of coupling of energy out of the waveguide.

21. An antenna according to claim 20, including short waveguide stubssurrounding each of the groups of holes and extending normally from saidone longitudinal wall, said waveguide stubs constituting fixed phaseshifters having different electrical lengths whereby the angularrelationship of the limits of the azimuth angle through which the fanshaped beam is scanned by movement of said ridge member, relative to avertical plane perpendicularly bisecting the waveguide, can be changed.

22. An antenna. according to claim 1, in which said elongated ridgemember is periodically segmented to structurally relieve stresses in theridge member when moved towards and away from said opposite side wall ofthe waveguide.

23. A radar antenna system comprising: an elongated horizontallydisposed waveguide for receiving electro magnetic energy in one end andhaving a series of holes in one longitudinal side wall dimensioned belowcut-off so as to be non-resonant and substantially insensitive to wavelength, said holes being arranged in first and second groups disposedalternately above and below the longitudinal center line of said onelongitudinal side wall, each group comprising a given number of holes inclosely spaced side by side relation along a given longitudinal distanceto define a given length for the group, the spacing between successivegroups being of the same order as said given length whereby energy iscoupled out of the waveguide to provide a fan shaped beam lying in avertical plane including broadside.

24. A radar antenna according to claim 23, in which said waveguide has aT shape in cross section; a ridge member in the stem portion of the Tshape; and means for moving the ridge member partially into andcompletely out of that portion of the waveguide defined by the cross ofthe T shape, the stem of the T shape being sufficiently long that saidridge member is moved into the stem so that its leading edge is movedbelow the cross of the T shape to a negative" ridge position, themovement of the ridge member effecting a scanning of said fan shapedbeam, through an azimuth angle on either side of broadside.

1. A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combination: a. an elongated horizontally disposed waveguide forreceiving electro-magnetic energy in one end and having a series ofholes in one longitudinal side wall dimensional below cut-off so as tobe non-resonant, said holes coupling energy out from the waveguide in amanner defining said fan shaped beam, the non resonant characteristic ofsaid holes rendering the shape of said beam substantially insensitive tofrequency variations over approxiMately a frequency octave; b. anelongated ridge member co-extensive with the length of said waveguidearranged to extend wholly within the guide along its length; and, c.means for maintaining the leading edge of the ridge in parallel relationwith the longitudinal axis of the waveguide while moving the ridgetowards and away from the opposite side wall of the waveguide to therebyvary the phase velocity of energy propagated along the waveguide in amanner to effect scanning of said fan shaped beam through said givenazimuth angle.
 2. A radar antenna system for radiating a fan shaped beamin a vertical plane and scanning the beam through a given azimuth angle,comprising, in combination: a. an elongated horizontally disposedwaveguide for receiving electro-magnetic energy in one end and having aseries of holes in one longitudinal side wall dimensioned below cut-offso as to be non-resonant, said holes coupling energy out from thewaveguide in a manner defining said fan-shaped beam; b. an elongatedridge member co-extensive with the length of said waveguide arranged toextend wholly within the guide along its length; and, c. means formaintaining the leading edge of the ridge in parallel relation with thelongitudinal axis of the waveguide while moving the ridge towards andaway from the opposite side wall of the waveguide to thereby vary thephase velocity of energy propagated along the waveguide in a manner toeffect scanning of said fan shaped beam through said given azimuthangle, said series of holes being arranged in first and second groupsdisposed alternately above and below the longitudinal center line ofsaid one longitudinal side wall, each group comprising a given number ofholes in closely spaced side-by-side relation along a given longitudinaldistance to define a given length for the group, the spacing betweensuccessive groups being of the same order as said given length wherebyenergy is coupled out of the waveguide in such a manner that said givenazimuth angle of scan passes through and on either side of a verticalplane bisecting the waveguide at its mid-point and orientedperpendicularly to the longitudinal axis of the waveguide.
 3. An antennaaccording to claim 2, in which said one longitudinal side wall includesrecessed areas to define reduced thickness portions surrounding thegiven number of holes making up the groups to increase the efficiency ofcoupling of energy out of the waveguide through the holes.
 4. An antennaaccording to claim 3, in which said elongated waveguide constitutes anintegral extrusion in the form of a T in cross section, the stem of theT accomodating at least a portion of said ridge, the broad side wallopposite the ridge constituting said one longitudinal side wall havingrecessed areas and said series of holes, said extrusion further definingintegral upper and lower longitudinal flanges extending forwardly fromthe upper and lower edges of the said longitudinal side wall to defineextended conductive surfaces guiding the coupled out radiant energy in aforward direction and further defining securing means for facilitatingthe mounting of the waveguide in the leading edge of an aircraft wing,the entire extrusion minimizing any leakage of electromagnetic energy inportions of the waveguide other than the holes.
 5. An antenna accordingto claim 4, including an elongated plastic means extendinglongitudinally between said upper and lower flanges in surface contactwith said one longitudinal side wall, said plastic means includingportions filling said recessed areas, the dielectric constant of theplastic means having a value to effect an optimum coupling of the energypassing from the waveguide to free space.
 6. An antenna according toclaim 4, in which said extrusion further defines longitudinal lighteningpassages running parallel to and on either exterior side of the narrowsides defined by the rectangular waveguide, whereby when said waveguideis mounted in the leading Edge of an aircraft wing, hot air can bepassed through said passages to heat said extrusion and serve as ade-icing means for the wing.
 7. An antenna according to claim 5, inwhich said elongated plastic means includes a conductive path followinga circuitous route to pass between said portions filling said recessedareas on either side of a center line from one end of the plastic meanstowards the other such that current can be passed through the conductivepath to heat the extrusion and serve as a de-icing means for the wing.8. An antenna according to claim 1, in which said waveguide is T shapedin cross section, said one longitudinal side wall having the series ofholes constituting a broad side wall, said ridge member being positionedin the stem of said T shape for movement towards and away from saidbroad side wall, said means for maintaining the leading edge of theridge member in parallel relation with the longitudinal axis of thewaveguide while moving the ridge towards and away from the broad sidewall, including: a. a series of rods rigidly secured at first ends tothe trailing edge of the ridge member at evenly spaced longitudinalpoints, the other ends of the rods passing through bearing openings inthe stem of the T shape; and b. a driving means coupled to said otherends of the rods for reciprocating them in unison back and forth in thehousing to thereby move the ridge towards and away from said broad sidewall, the ridge member itself and rods being held out of physicalcontact with the T shaped waveguide other than at the bearing openingsso that it is ''''floating.''''
 9. An antenna according to claim 8, inwhich the stem of the T shape is sufficiently long that said ridgemember can move freely within the stem to a ''''negative'''' ridgeposition with respect to a conventional rigid ridged waveguide shape.10. An antenna according to claim 8, in which said driving meansincludes means for reciprocating said rods to follow a linear motionover a major portion of their travel in each direction.
 11. An antennaaccording to claim 1, having an input energy transition structure forpassing said electromagnetic energy into said one end of said waveguide,said input transition structure including: a. an input waveguide sectionhaving a transition ridge section pivoted at one end to the co-extensiveend of said ridge member in the waveguide, and having its other endcoupled to be flush with one wall of said input waveguide section suchthat a gradual diminution of the effect of the ridge member is providedfor any given position of the ridge member; and b. an expandingwaveguide coupling section with its converging end coupled to the inputwaveguide section, and its expanded end receiving input electromagneticenergy.
 12. An antenna according to claim 1, having a terminationtransition structure for providing a proper termination impedance forenergy passing towards the other end of said waveguide, said terminationtransition structure including: a. a termination waveguide sectionhaving a closed end and a transition ridge section pivoted at one end tothe end of the ridge member co-extensive with said other end of thewaveguide, and having its other end coupled to be flush with one wall ofsaid termination waveguide section such that a gradual diminution of theeffect of the ridge member is provided for any given position of theridge member; and b. a wedge-shaped section of ferrite material on thewall of the termination waveguide section opposite to the transitionridge section to minimize reflections of energy at said other end of thewaveguide.
 13. An antenna according to claim 1, having an input energytransition structure for passing said electromagnetic energy into saidone end of said waveguide, said input transition structure including: aninput waveguide section including a transition ridge sectionconstituting an integral extension of the ridge member, said extensionhaving itS upper edge tapering towards its lower edge and including aplurality of slots to define ridge projections decreasing successivelyin height, the floor of said waveguide section including a series ofwindows through which said ridge projections extend when said ridgemember is moving in the waveguide to thereby provide a gradualdiminution of the effect of the ridge member for any given position ofthe ridge member.
 14. An antenna according to claim 13, in which saidinput energy transition structure includes an expanding waveguidecoupling section with its converging end connected to said inputwaveguide section and its expanded end receiving input electromagneticenergy.
 15. An antenna according to claim 13, in which said inputwaveguide section expands in size from its end coupled to the waveguideto its end receiving input electromagnetic energy.
 16. An antennaaccording to claim 1, having a termination transition structure forproviding a proper termination impedance for energy passing towards theother end of said waveguide, said termination transition structureincluding: a termination waveguide section having a closed end and atransition ridge section constituting an integral extension of the ridgemember, said extension having its upper edge tapering towards its loweredge and including a plurality of slots to define ridge projectionsdecreasing successively in height, the floor of said terminationwaveguide section including a series of windows through which said ridgeprojections extend when said ridge member is moving in the waveguide;and a wedge-shaped section of ferrite material on the wall of thetermination waveguide section opposite to the transition ridge sectionto minimize reflections of energy at said other end of the waveguide.17. An antenna according to claim 1, having an input structure forpassing electromagnetic energy into said one end of said waveguideincluding: an input waveguide section including a ridge sectionconstituting an integral extension of said ridge member, the upper wallof the waveguide section opposite said ridge section having a coaxialline connected thereto, the outer conductor of the line terminating atthe wall and the inner conductor extending into the waveguide towardsthe top edge of said ridge section, said inner conductor terminatingshort of the ridge section; movable tuning probe means extending intosaid wall of the waveguide section between the inner conductor and thepoint of connection of the waveguide section to said waveguide; andmeans mechanically connecting the tuning probe means to said ridgemember for movement with the ridge member whereby input electromagneticenergy in said coaxial line is transferred to said waveguide withmaximum coupling efficiency for every position of the ridge member. 18.An antenna according to claim 1, having a termination transitionstructure for providing a proper termination impedance for energypassing towards the other end of said waveguide, said terminationtransition structure including: a wedge shaped section of ferritematerial on the wall of said other end of said waveguide opposite theco-extensive end portion of said ridge member; and a metallic end wallclosing the said other end of the waveguide, the wedge shaped sectionminimizing reflections of energy at said other end of the waveguide. 19.A radar antenna system for radiating a fan shaped beam in a verticalplane and scanning the beam through a given azimuth angle, comprising,in combination: a. an elongated horizontally disposed waveguide forreceiving electro-magnetic energy in one end and having a series ofholes in one longitudinal side wall dimensioned below cut-off so as tobe non-resonant, said holes coupling energy out from the waveguide in amanner defining said fan-shaped beam; b. an elongated ridge memberco-extensive with the length of said waveguide arranged to extend whollywithin the guide along its length; and, c. means for maintaining theleading edge of tHe ridge in parallel relation with the longitudinalaxis of the waveguide while moving the ridge towards and away from theopposite side wall of the waveguide to thereby vary the phase velocityof energy propagated along the waveguide in a manner to effect scanningof said fan shaped beam through said given azimuth angle, said series ofholes extending longitudinally between the longitudinal center line andone edge of said one longitudinal wall in closely spaced side-by-siderelationship, the portion of the wall through which the holes pass beingrecessed to provide a reduced thickness portion to increase theefficiency of coupling of energy out of the waveguide.
 20. A radarantenna system for radiating a fan shaped beam in a vertical plane andscanning the beam through a given azimuth angle, comprising, incombination: a. an elongated horizontally disposed waveguide forreceiving electro-magnetic energy in one end and having a series ofholes in one longitudinal side wall dimensioned below cut-off so as tobe non-resonant, said holes coupling energy out from the waveguide in amanner defining said fan-shaped beam; b. an elongated ridge memberco-extensive with the length of said waveguide arranged to extend whollywithin the guide along its length; and, c. means for maintaining theleading edge of the ridge in parallel relation with the longitudinalaxis of the waveguide while moving the ridge towards and away from theopposite side wall of the waveguide to thereby vary the phase velocityof energy propagated along the waveguide in a manner to effect scanningof said fan shaped beam through said given azimuth angle, said series ofholes being arranged in groups serially extending between thelongitudinal center line and one edge of said one longitudinal wall,each group comprising a given number of holes in closely spacedside-by-side relation along a given longitudinal distance to define agiven length for the group, the spacing between successive groups beingof the same order as said given length, the longitudinal wall includingrecessed areas to define reduced thickness portions surrounding thegiven number of holes making up the groups to increase the efficiency ofcoupling of energy out of the waveguide.
 21. An antenna according toclaim 20, including short waveguide stubs surrounding each of the groupsof holes and extending normally from said one longitudinal wall, saidwaveguide stubs constituting fixed phase shifters having differentelectrical lengths whereby the angular relationship of the limits of theazimuth angle through which the fan shaped beam is scanned by movementof said ridge member, relative to a vertical plane perpendicularlybisecting the waveguide, can be changed.
 22. An antenna according toclaim 1, in which said elongated ridge member is periodically segmentedto structurally relieve stresses in the ridge member when moved towardsand away from said opposite side wall of the waveguide.
 23. A radarantenna system comprising: an elongated horizontally disposed waveguidefor receiving electromagnetic energy in one end and having a series ofholes in one longitudinal side wall dimensioned below cut-off so as tobe non-resonant and substantially insensitive to wave length, said holesbeing arranged in first and second groups disposed alternately above andbelow the longitudinal center line of said one longitudinal side wall,each group comprising a given number of holes in closely spaced side byside relation along a given longitudinal distance to define a givenlength for the group, the spacing between successive groups being of thesame order as said given length whereby energy is coupled out of thewaveguide to provide a fan shaped beam lying in a vertical planeincluding broadside.
 24. A radar antenna according to claim 23, in whichsaid waveguide has a T shape in cross section; a ridge member in thestem portion of the T shape; and means for moving the ridge memberpartially into and completely out of that portion of The waveguidedefined by the cross of the T shape, the stem of the T shape beingsufficiently long that said ridge member is moved into the stem so thatits leading edge is moved below the cross of the T shape to a''''negative'''' ridge position, the movement of the ridge membereffecting a scanning of said fan shaped beam, through an azimuth angleon either side of broadside.